1. Field of the Invention
This invention relates to an abnormality detection apparatus of a comparator in a control circuit equipped with a microcomputer.
2. Description of Related Art
A comparator has been widely used in various input systems to a microcomputer in a control circuit equipped with the microcomputer. For example, the comparator compares voltages of signals from an input circuit that are inputted to two input terminals, and sends a comparison result as an H or L level output from an output terminal to an input port of the microcomputer.
Such a comparator includes a large number of terminal pins at its input/output terminals in addition to terminals of a driving power source system, and involves the possibility of open-circuit failure or short-circuit failure between the comparator main body and the terminal pin and failure in peripheral devices. Such failure in and around the comparator becomes an error input to the microcomputer and hinders normal control.
It is therefore necessary to confirm whether or not circuits in and around the comparator normally operate. Though a technology has been practiced in the past that takes out the comparator single body and confirms its basic operation, it has been difficult to confirm the comparator operation under the state where the comparator is used inside the control apparatus. When hysteresis is imparted to the comparator, means has not been available for detecting failure of the peripheral devices for imparting hysteresis.